Spark check arrangement



Sept. 12, 1944.

S. G. ISSERSTEDT SPARK CHECK ARRANGEMENT Filed Feb. 12, 1942 no mmvrox ia-gfriea. G. Inez-steak" BY Attorner Patented SeptII Z, 1944 a I 7 I 2,358,166

I Siegfried G. Isserstedt, Minneapolis, "as Signor to Minneapolis-Honeywell Regulator of Delaware Company, -Minneapo-lis, Minm, a corporation- Application February 12, IMLZ Sie-rial No; $6,641

Claims. (01. 158-28) The present invention is directed to an automatic control system for fluid fuel burners in which the fuel is ignited by means of an electric spark. The present invention is an improvement over the type of system shown in the patent to 5 Koerner 2,143,076. The systemcovered in Koerner isa system which will check the spark gapfor igniting the fuel at the burner so that if the gap is too small so as to'cause a substantial short circuit, or if 10 this gap is so wide as to not produce the proper: :l

spark; it will be impossible to energize the burner motor. Various different modifications are shown but in each modification it is necessary to utilize two separate relays, one responding to a substane, tial short circuit in the spark gap circuit and the;

other responding to a very low value of current in the spark gap' circuit due to'the electrodes being too widely spaced. The two relays are controlled in each case by means of a leakage transformer which also feeds power to the high voltage 1 spark gap circuit; v

One ofthe main objects of the presenti'nvention is to accomplish thesame results as are accomplished by Koerner with the us'eof a single relay which will close the switch to the burner" motor if the current. flow through the relay is within a predetermined range, but which will. maintain this switch in open position if the current flow through the relay is either above or below this predetermined range. g

'An additional object of the invention is to design a double armature relay which will operate to'attract one of its armatures when the current new therethrough is within a predetermined 5 range for the'purpose of closing a switch, and.* which 'will energize a second armature when the current flow through the relay exceeds a predetermined high value, the second armature'operating to open the switch. 40

A further object of the invention is to provide means for locking the burner motor switch in' open position in the event it has been opened as a result of the spark electrodes being spaced too widely apart. The purpose of this is to prevent V winding 22 of the; relay indicated generally at the burner motor from being intermittently energized and deenergi'zed in the event the spark should appear and'dis-appear between the electrodes,

A further objectof theinvention isto design an electromagnet'relay in which a main arma-V ture will move a movable contact intolxengagement with a stationary contact when it. at-

tracted; and an'auxiliary armature "which will the stationary contact when it is attracted due to an increase in theflow of current through the relay above a-predetermined' high value.

A still further object of theinvention is to design arelayof the above type in which the auxiliary :armaturemoves the stationary contact out of engagement with'the movable contact when the auxiliary armature is attracted due-to a predetermined high flow of current throughthe re- A still further object of the invention is\ to providethe relay with a trip which is released by the auxiliaryarmature to prevent this armatu-re from: returning to its original position and reclosing the switch.

r These and: other objects will readily become ap-. parent as the following specification is read in the w A lightof the accompanyingdrawing in which:

Figure 1 is a moreor less; diagrammatic rep- 20 resentation of a system. incorporating the various features of my invention; and

, Figure 2- is a. view of aslightly modified form of relay which may be substituted for the relay shown in Figure 1, 4

The control system shown in-Figure 1 is adapted to control electrically the delivery of a fluid fuel to a burner-,1 and to provide electrical means for igniting the fuel so delivered.- It will be understood that: many different typesof fluid fuel maybe used and that many different types of electrical means may be used for controlling the delivery of fuel; I-Iowever, ,for the purposes of illustration theelectrical; means for controlling the delivery of fuel is illustrated as the usual burner motor I I l-. 'A. pair of'electrodes name 13 are connected by means of conductors and I5 to a high voltage secondarywinding l6 of aleakage type transformer indicated genera1ly atjl'|.-

When this high voltage ci-rcuit is energized,'a

spark will 'jump between the electrodes l2 and l'3 for igniting the fuel delivered to the burner by the burner motor ll-. I

'The'transformer l-l isprovided with-an auxiliarysecondary winding 19 which is connected by means of the conductors and-2| to a relay 2 3., The relay-'23s is providedwith an armature armature 2 5 to itsunattracted-position in which the contact 2;! isoutlofengagementwith. the contact-18;- but when the relay eoi-rz-z is sufficiently move th'emovable contact out of eng'agementwit-h energized therarmature z-s'isattracted; thuscaus ing it to move downwardly and close the switch The center leg 42 is connected with the two side 21, 28. legs 44 and 45 which provide for a normal low.

The armature 25 carries a block of insulating reluctance path for the magnetic flux produced material, such as Bakelite, indicated at 3|]. A by the primary winding 43. The transformer I? second armature 3| is carried by the armature 5 has a leakage path which includes the cross leg 25 in a chamber formed by a cut-away portion 46 which is connected to the center leg 42 but in the bottom of theinsulating member 30 which whichjis separated from the two side legs 44 and registers with an opening through the armature 45 by an air gap. Normally therefore, the flux 25 as indicated at 32. The armature 3| is pro- I will flow through the center leg 43 and then vided with a stem which extends upwardly'm through the side legs 44 and 45. As long as the through an opening in the insulating member a "two electrodes l2 and I3 are properly spaced so 30 and connects to an L shapedoperating memas to produce a spark between them, a normal ber 34. The armature 3|,,stem 33 andoperatingZI- ,a unt of current'will flow thr u h the member 34 are all suitably conne'cted; together as Qo' a' y windin '6. The current induced in the a unit. A biasing spring 35 seats at its lo er secondary winding IE will set up magnetic flux.,

endon the insulating member 30 and at its upwhich will tend to Opp e the normal flow of per end against the L shaped operating member magnetic fillX p e by t e p y Winding 34 to bias the operating member and armature3| ro t e Center leg However, s o to itsunattracted position as shown in Figure 1. esrthe flow current in the se y winding VAsecond'block' finsulatin 'm t j l 311 I6 is normal, suflicient current will be induced rie'i on th upper surfa'c'e'of'the insulating mem i thes da ywi di s l9 o p duc a no al ber 30 is h u w 1 1; to o m i und now of current through the relay winding 22 with which lidably rec ive -tri m chan s 38; A ithe result that the armature 25 will be moved biasing spring 3 9 withinthe "cylinder-biases-the to itsfattracted position to close the contact 21, trip member 38 toward the "right-as seen in'r'igure 25 28. The flow of current through the relay wind 1 and itsengagement with the end-of the o ing 22 will at this time be insufficient to attract at member 34 'restr'ai s" this trip membe the second armature 3|, with the result thatith from furthermoyementi It will be understood Switch 28 will remain d. that if the armature 3| is attracted it will move 1 If theteleetrodes d it e spaced too close dow wa dly, carrying the o'perating-member 34 30ftcgether and do not produce a spark then the with it, and the operating me'rnber 34 will th n circuitin which they are located will be effecrelea e th trip member-33 "for m v t fithe tively short circuited withtthe result that an abright The trip m r. be normally large current will flow through the secmediately above the operating member 34 and 3 Winding 5. iaw p od ce 1 V y will therefore lock the armature 3| in its ener- 35- e of flux which bucks the flux p gized-pos'itionand prevent its' t m m tducedbythe primary winding 43. Under these tracted position. The armature 3| then must 'conditions the major portion of t flux W l p ss f remain in this position until the trip member 38 *thmughthe leakage P 45 a o y a Sma l i pulled b k t t r iiie p t s" 7' ,current will be induced in the secondary winding of the knob w, at whi h-tim thbjagjng Spring 40 19. and therefore the flow of current through the win b rb at et f 'ai e m u to relay 22 is so slight that the relay is unable to its unattract d po on t etu n th rt' t pull in-the armature 25 with theresult. that the the position shownin Figure 1 7 switch 21, 28 will remain open.

If the urr t fle th t e el zg is If the-two electrodes 2 and 3 are so widely radually increased iro'm-z r'oto a certain value, Spaced that they do t p e t pr p r the relay will attract the armature 25 and cau e Spark, then the current flow through the secondit tomove to the position shown in dotted lines Winding Will be Very Small n as a in' the drawing in which the contact 21 and 2s Sult a much la e fl w l flow t r e will h in g gfe t; If th current center leg .42 and induce an abnormally large through the coil 22 i then'increased further-Ito Current in theseeondery d g is a a predetermih 'dhi l the a t 3 w normally large current flow through the relay b attracted to pull the, operating be 34 coil 22-will not only attract the armature 25 but downw dl "I1'1e' jpergtipg member 34 wfll f will also attract the second armature 3|;which, gage the resilientblade 4|;on which the t t en: 7 as explained abo've,'will cause the operating meme ary contacty28, -is"mounted and will cause this 55.ber 34 toengage the resilient blade 4| and move blade'to movem rm te t e n- 1 the :contact 28 out of engagement with the contact 28" from contact 2li At the sometime the 43am? I trip'member 38wil1 be released and the armature It will therefore b n that the Switch Z7, 28 3| will be locked in its lower positionv so that Will be closed by the relay win i g 2 y when even though the relay 22 were deenergizediand t electrodes and are Spaced so as to then energized again it wouldbe inoperativ t duce a proper spark and cause a normal current cl se.th it h 21 zg d i t fa t that t .flow' through the secondary winding l6 which 7 operating embe 34. would n s' i :Causesanormal-current to be induced in the position and wou d push 'the res i-lient blade 4| Aeeeondery winding! 9 n fed to the relay Winddownwardly and t e pf ve ti 5 ing22. If the current flow through the relay tact 21 from engagi'ng the stationary contact 28 winding 22 should be either lower or higher than Therefore, before the switch-21, 28 can aga'ir'i b -the' normal range of'current' values, then either closedit is necessarytopullthe trip membei-BB the armature 25 will notice pulled in, or both to thele'ft by means of the knob 40'to'permit l the armature '25 and the armature 3| will be 'thebiasin spring 35't t n th a at 3 .Tupulled in. In either casethe'switch 21, 28 will tofits unattractedposition; f 'j'- e 7 v befopened. a V e -""Reierring'nowfto'ithe transformer |'|,-itwill-be "The energization of 'the primary winding 43 s fe en tha't this transiormer consists' of. acent'er i of the transformer ll 'is'under the control'of a "leg 42 oii which a primaryw-inding'fl as well as switch formed by therelay arm5t) and stationary the two secondarywindings Hi and I9 arewound. 75 contact 5|, the" re1ay a m 59 b i g p y "means of the armature, indicated by the dotted line 52, of an electromagnetic relay having a relay winding 53.

The armature 52 additionally controls the relay arm 54. .When the relay winding- 53 is energized, the armature is attracted to move the relay armsll and 54 into engage ment with their stationary contacts 5| and 55, and when the relay winding .53 is deenergized these relay arms move out of 'ergagement with their stationary contacts. a

The energization of therelay Winding 53 may be controlled" manually or it may be placedunder the control of any one ofanumber of different'types of condition responsive devices. For

- purposes of illustration" however, this relay has been shown as being under the control of a thermostat indicated generally at 51 which comprises a bimetallic element 58 which is fixed atone end and which carries at its free end a pair of I contact blades 59 and 65 which cooperate with the stationary contacts 6| andBZ, respectively. The arrangement is such that one decrease in temperature the resilient contact bladev 59 is first brought into engagement with itsstationarycontact BI and then at a slightly lower temperature the contact blade 56' is brought into engagement with its stationary contact 52. I

This system is'provided with the usual time switch which is commonly known as a-safety switch and which is indicated generally at 65.

It is composed of a pair of resilient contact blades 66 and Bl'which are biased to open' position and which are latched in closed position by the "free end of a thermal blade 68. The thermal blade (i8 is adapted to be heated by means of the elec-"' tric heater 69' andwhen so heated warps toward the right and after a predetermined time interval releases the resilient contact blade 67 for movement downwardly to open circuit position. The safety switch then remains in this position mary winding- 8| and arse'condary winding 82,

the primary'winding 8| being connected by jmeansof'conductors 83 and 84 to the line wire a 85 and the line wire 86;

Operation The various elements of the control system are shown in Figure 1 in the positions which they will occupy when the room. thermostat 51 is satisfied and therefore holding the two contact blades 59 and 60 out-of engagement with their respective stationary contacts GI and 62. The relay winding 63 will therefore be deenergized and the I a h gagment with the contact 14.

I The temperature in the space inwhich the thermostat 51 l S located will therefore begin to decrease andthe bimetallic element 58 will contract and cause'the switch blade 59 toengage the stationary contact 6|. This action will not 7 result in the establishment of any circuit at this until it is manually reset by the reset button .10.

The reset button Hi provides what-is known as a trip free reset, that isi't maintains the contact blades '56" and lil-in'open circuit'pos'ition during the resetting operation sothat the'safety switch cannot be closed until the button '10 is released and then not unless'the thermal blade 68 has cooled off and returned to a position' where it y can engage the contact blade 6"! and latch the 7 switch in its closed position.

A combustion responsivedeviceindicated gen erally at I2 is provided for responding to the presence or absence of combustion at the burner. This device has a pair of cold contacts53a'nd M whi'c'hare engaged by the contact'blades -15 and ing 82) time due to'the fact that the relay arm 54 isout ofengagement with its stationary contact 55. Upon a further decrease in temperature, the bimetallic element 58 will cause the switch blade 69 to engage its stationary contact 62. This will result in the energization'of relay winding 53 by rneansof a circuit extending from one side of. the secondary winding 82 through conductor 88, a

contact. 6!, switch blades 59 and 60, contact 62, conductor 89; contact 14; switch blades 16. and 15, contact'13-,-conductor 90, electric heateriiq, conductor 9|; relay winding 53, conductor 92, safety switch blades 6? and-6'6, and conductor 93 baclr to the other side ofthe .secondary wind- Closure of this circuitwillcause the relay Winding 53 to attract the armature 52 which willin turn move the relay arms and 5! to closed 7, circuit position. Engagement of the relay arm .54 with its contact will establish aholding" 50o frornone side of the secondary winding 82 circuit for the'relay winding 53 which extends through conductor 88, contact 6!, contact blade,

I 59, bimetallic element 58,"conductor 95, relay arm 54, contact 55, conductor 96, contact blade '55.

56 in the absence of combustion at-the burner, 1

and a hot contact Tl which engaged by' the switch blade 18 when combustion is present-at 'COntEtCbyH, conductor 99, electric heating element 69, conductor 9l ,-*relay winding 53; conductor'92', safety switch blades 61 and 66,-and

the burner. The switching action-of this device, I

overlaps on heating butnoton cooling. That is, on heating'the contact blade- 18 engages; the stationary contact ll before the contactlblade l5 leavesthe stationary'conta'ct 13, but on cooling the contact blade 'Hlfirst separates fromxstationary contact 1'! and then the contactblade l5 'engagesthe stationary contact '53. Alsothe arrangement is' such that the contact blade :15

; does .not engage: its stationary contact m until after the contact bladejlfi hasmovedinto vengagement with the stationaryi'contact 13. Such devices are old and Well known and maybe purchased on the open market-and a f urther description thereof is- 'notbelievednecessary.

v The electrical power,forthe control system is .provided fromra transformer efljhavingna; pri-1 conductor 93..back to'theother side of the secondary winding -82. It will be noted that this holdin'gcircuit for the relay winding 53 is independent of the switch blades 63 and. '|6.'jIt wi1l be noted also-that both the original energizing .circuit for the relay winding 53 as well asthe holding circuit includes the electric heating element 59 which starts heating the bimetallic; blade 7 58, so that after a predetermined period of time also cause movement-of therelay arm 5,0 tocliised V this blade will warp toward the right and open the safetyswitch 66, 51 which will terminate the supply of electric power to the entire system.

The energization of'th'e relay winding 53 will 7 circuit-position-which will-cause energi zationg'of the primary winding1j43 of the transformer I?" iby'rneans ofaccircuitlextending from line'wire 86 through conductor-98; contactiil, relay arm 5i3,

'I'he energization of the primary winding I 43 causes current to be induced in both of the secondary windings I6 and I9 and, as set forth above, the amount of current induced in the secondary winding I9 depends upon the amount of current that as long as the switch 21, 28 operated by the relay 23 was in open circuit motor I I is deenergized.

Let it be assumed first that the primary winding 43 of the transformer I1 has just been energized as a resultof the call for heat by the thermostat and that at this time there is a sub-v stantial short circuit between the electrodes I2 and I3 with the result that they do not produce a proper spark for igniting fuel atthe burner;

position the burner Under these circumstances, an abnormally large current will flow in the circuitincluding the secondary Winding I6 and the counterflux generated I thereby Will cause most of the flux produced by the primary winding 43 to flow through the leakage path 46 with the result that only a very small current'will be induced in the secondary winding I9. This small current flow through the relay coil'22 will be insufficient to produce a magnetic force great enough to attractthe armature 25 and the switch 21, 28 will therefore remain in open circuit position and theburner motor will remain deenergized. Therefore, when the electrodes 'I2 and I3 are inoperative to produce a spark'for igniting the fuel due to their being substantially short circuited the burner motor I I will not be energized'and no fuel will bedelivered to the burner. Combustion will not be produced and therefore the combustion responsive device I2 will remain in its cold position in whichthe contact blade I5 will remain in engagement with its cold contact 13. The thermostat 51 will still be calling for heat and therefore the relay winding 53 and the electric heater 69 will remain energized. After a predetermined period of time the bimetallic'blade 68 will have heated sufficiently to open the safety switch 66, 68 which will terminate the supply of power to the system. The system will then remain locked.

out until the safety switch 66, 6! is manually reset, and before this is done it is assumed that the difiiculty which prevented combustionwill have been corrected. a

Let it be assumed now that the space between the electrodes I2 and I3 is proper andthat a proper spark is produced. Under these circumstances a normal current will flow throughthe conductors 99-and loo, primary winding 43 and conductor IOI back to the other line wire 85.

blade I5 disengages the cold contact I3.. This will cause a holding circuit for the relay winding 53 to be established, this holding circuit extending from one side of the secondary winding 82 through conductor 88, contact BI, switch blade 59,'bimetallic' element 58, conductor 95, re-

.lay arm 54, contact 55, conductor 96, switch blade I8, hot contact II,'conductors I91 and 9I, relay winding 53, conductor 92, safety, switch blades 61 and 66, and "conductor 93 backto the other side of the secondary winding 82. It will be seen that the establishment. of this circuit effectively short-circuits the electric heating elevment 69 and that therefore this element will be deenergized even before the combustion responsive'device I2 causes the switch blade I5 to separate from the cold contact I3. The relay winding 53 will therefore remain energized as well as the primary winding 43 of the transformer I I and the relay winding 22. The burner motor switch 21, 28 therefore remains closed. This is the running condition of thesystem.

If the electrodes I2 and I3 should be spaced properly to form the proper spark and the burner motor .21, 28 therefore closed but for some other reason combustion should not be established then the combustion responsive devicefIZ would not cause the switch blade I8 to engage the hot contact I2 and therefore the electrical heating element 69 would remain energized and cause the safety switch 66,61 to open after a predetermined 7 period of time. Here again, the-system could not be automatically restarted until the safety switch is manually reset, and this would be done only when the trouble which prevented the establishment of combustion was corrected,

Let it be assumed now that the relay winding 53 and primary winding 43 of the transformer I! have just been energizedin response to a call for heat by the thermostat 5! and that the electrodes I 2 and I3 are so widely spacedas to not produce a proper spark for establishing combustion. Under these conditions, a very small current will flow through the secondary winding I6 which will cause a very large current to be induced in the secondary winding I9. The abnormally large current flow through the relay winding 22.will not only cause the armature 25 to be attracted but will also cause the armature 3| to be attracted with the result that the operating member 34 will be pulled downwardly to move the stationary contact 28 away from the movable contact 21. Under 7 these conditions the burner motor II will not be energized and combustion at the burner. will not be established. Therefore, the combustion responsive device I2 will remain in its cold position and the bimetallic blade 68 will warp toward the right and open the safety switch 66,-61 as before. It sometimes occurs'that when the electrodes I2 and I3 are spaced a little too widely apart they may still produce a spark and cause a sufiicient secondary winding I6 and likewise a normal cur- 7 rent will be induced in the secondary winding combustion will ,be established and the combusflowof current through the secondary winding I6 to cause a normal current to be induced in the secondary winding I9 and hence flow through the I relay winding 22. 'Under these conditions therefore, the armature 25 will be attracted andclose the switch 21, 28 to energize the burner motor II.' Inasmuch as-the electrodes I2 and I3 are a little toowidely'spacedtheenergization of the burnermotor' II in blowingthe vaporized oil from the nozzle of the burner may blowout the spark 7 between the electrodes I2 and I3 vwith'the result tion responsive device I2 will cause the switch; blade I8 to engage its hot contact I9 before the that the current'fiow through the secondary coil 16 will take a sudden'drop and therefore cause an abnormallylarge current to flow through the relay coil 22. This will attract the armaturefil and cause the operating member'34 to open the switch 21, 28, andtherefore deener'gizetliefburner motor H. The stopping of the burnermoto'r H may again cause thejproductio'n of a"s'p'a rk between the electrodes l2 and "l 3 to" reduce the current flow through th'e'r'elay winding 22"to a normal value again. Therefore, unless somefmea'ns were provided for preventing it the "armature 3| would be released and the burner motorswitch 2'1, 28 would close and r'e'en'ergize'the" burner motor I land the cycle wouldrepeatitself' over'and over again. In order to'prevent this, the trip member 38 has been provided so that when thear'mature 3! has been pulled 'indue to an abnormally large current fiowing'through the 'relay'coil 22, it cannotbe released until"thetrip'member- 38 -has been removed manually. Thus, the burner motor switch 21, 28 will remain open and the burner motor H will remain deenergized so that after a predetermined period of time the bimetallic element H will warp to the right and trip the safety switch 66, 6'! to open circuit position.

Figure 2 shows a slightly modified form of relay which may be substituted for the relay 22 of Figure 1. A relay coil H is adapted to attract armature H2 which is pivotally mounted on bracket Ill and biased to its unattracted position by means of a biasing spring shown at H3. The armature H2 carries a movable contact H4 by means of a resilient blade H5, the movable contact being adapted to cooperate with a stationary contact H6. The relay armature H2 is shown in its attracted position in which the movable contact H4 is in engagement with the stationary contact H6. The armature H2 pivotally carries a second armature H1 in the form of an angled lever mounted beneath the resilient blade H5. It will be clear that when the current flow through the relay coil I it reaches an abnormally high value the armature I I! will be attracted and rotated in a counter-clockwise direction so that the end H8 will lift the resilient contact blade H5 and cause the movable contact H4 to separate from the stationary contact H6. No trip mechanism has been shown in this modification for locking the switch H4, H6 in open position but it will be obvious that such a mechanism could be added to this relay without the exercise of invention.

Many changes and modifications in this invention will doubtless occur to those who are skilled in the art, and I therefore wish it to be understood that I intend to be limited only by the scope of the appended claims and not by the specific embodiment which has been disclosed herein only for the purposes of illustration.

I claim as my invention:

1. In a fluid fuel. burner control system, in combination, a switch which, when closed, causes the delivery of fuel to a burner, an electric circuit, means responsive to the current flow in said circuit for closing said switch when said current flow is within a predetermined range, means including a transformer for delivering power to a high voltage circuit supplying a sparking device for igniting the fuel delivered to the burner, said transformer including means for varying the current flow in said electric circuit in accordance with the current flow in said high voltage circuit, the arrangement being such that when the flow of current in said high voltage is normal the flow of current in said electric circuit will be within said predetermined range, but when the current flow in said high voltage circuit is abnormally high or low the current flow in said electric *circuit will be -below "or "above said prede "rz'nfined *rang'e espctively, and means for lockingfisaid iiiopen position when the current "in said ectric cireuit rises above said ereae einimee-mnge. i s 7 2. A' sparkcheck-syste'm "for fluid fuel burners comprising in combination electricauy l operative means for delivering uel to a burner, a high voltage "circuit including a 'spark-g'ap for'igniting the fuelgan energizing cir'cuit for'said fuel delivery means, a normally open switch controlling a e icir'c uit, an electric -elay for operating said switcna *ci'lcuit fonsaid *rela-y, sa d ren operating to close said svvi'tchwhen ithe' -current in sa rray circuit a es-eds a fi'rst v'alue, means including a' tr'ans form rwnmn-smpues power to said hi'gh voltage *eireuitana 'relaycircuit for Varying the current flow in said relay circuit in accordance with current flow in said high voltage circuit, the arrangement being such that the flow of current in said relay circuit exceeds a second higher value when the spark gap is too wide and is less than said first value when there is a substantial short circuit in said high voltage circuit, means operated by said electric relay for opening said switch in the event that the current through said relay should exceed said second value, and trip means released by said last named means for preventing reclosure of said switch until said trip means has been manually reset.

3. A spark check system for fluid fuel burners comprising in combination, electrically operated means for controlling the delivery of fuel to a burner, a high voltage circuit including a spark gap for igniting the fuel, an energizing circuit for said fuel controlling means, a normally open switch controlling said circuit, an electric relay for operating said switch, said relay comprising a relay coil and two armatures actuable in succession as the current through said relay coil increases, a first of said armatures being actuated when the current through the relay coil rises 7 above a first value, a second of said armatures being actuated when said current increases above a second value, said first armature being effective when actuated to close said switch and said second armature being effective to open said switch, and means including a transformer which supplies power to'said high voltage circuit and relay coil in accordance with current fiow in said high voltage circuit, the arrangement being such that the flow of current through said relay coil is between said first and second values only when the spark across said spark gap is of the proper character for igniting the fuel.

4. A spark check system for fluid fuel burners comprising in combination, electrically operated means for controlling the delivery of fuel to a burner, a high voltage circuit including a spark gap for igniting the fuel, an energizing circuit for said fuel controlling means, a normally open switch controlling said circuit, an electric relay for operating said switch, said relay comprising a relay coil and two armatures actuable in succession as the current through said relay coil increases, a first of said armatures being actuated when the current through the relay' coil rises above a first value, a second of said armatures being actuated when said current increases above a second value, said first armature being effective when actuated to close said switch and said second armature being effective to open said switch, and'means including a transformer which supplies power to said high voltage circuit and relay 6 v o coil in accordance with current flow in said high voltage circuit, the arrangement being such that the fiow of current through said relay coil is between said first and second values only when the spark across said spark gap is of the propercharacter for igniting the fuel, said relay being provided, with means efiective when said second armature is actuated to latch said second armaturegin ja position with respect to said first armai cuit for closing said switch when said current flow is within a predetermined range, means ineluding a'transfoimr for delivering power to a high voltage circuit supplying a sparking device for igniting the fuel delivered to the burner, said transformer including means for varying the current flow in said electric circuit in accordance with the-current flow in said high voltage circuit, the arrangement being such that when the flow of current in said high voltage is normal the flow of current in said electric circuit will be within said predetermined range, but when the current flow -in said high voltage circuit is abnormally high or low the current flow in said electric circuit will be outside of said predetermined range, and means for locking said switch in open position when the current in said electric circuit rises above said predetermined range.

SIEGFRIED G. ISSERSTEDT. 

